Male professional players have longer legs & are better at endurance running than female players. A mixed system would create a male-dominated pro league and a mixed secondary league. This would be no better than the present, and would cast the female players in an unnecessarily bad light.
A better option would be to separate players by height class, analogous to weight class in other sports. This would move short male players into the previously-female league & tall female players into the previously-male league. It's more rational and less restrictive than the gendered version.